- An Australian study using data from more than 15,000 adults found that where people live explained about 15.5 per cent of differences in body mass index between areas.
- When people moved, their weight gradually shifted towards the average body mass index of their new area, especially in the first few years after relocation.
- Place effects were strongest when comparing regions with different access to fruit and vegetable shops and different food environments, suggesting that policy changes to local environments could support healthier weight.
Researchers analysed data from a long running national survey that has followed Australians since 2001.
They focused on the years 2006 to 2019, when body mass index information was available and before the disruption of the COVID 19 pandemic.
The team identified 15,620 adults, giving almost 100,000 observations.
Some stayed in the same area, others moved once to a different postcode.
Movers were the key group, because their weight could be tracked before and after relocation.
Using a dynamic event study design, the authors examined how much a person’s body mass index shifted towards the average of the new area after moving, while accounting for previous trends.
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What they found
On average, about one sixth of geographic differences in weight could be attributed to where people live rather than their personal characteristics.
In statistical terms, there was a 15.5 per cent convergence towards the average body mass index of the destination area after a move. The effect was stronger in women than in men.
The influence of place was larger when comparing areas with particularly high or low body mass index levels, or with very different levels of access to fruit and vegetable stores and other food outlets.
Changing location also altered patterns of grocery spending and eating out, but had little effect on self reported physical activity.
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What this means for policy
This work supports the idea that local environments matter for weight.
Food access, prices, marketing and neighbourhood design all appear to nudge people towards certain habits over time.
The authors stress that personal factors still explain most of the variation in body mass index, so environment is not destiny.
However, if policy makers want to reduce obesity and diabetes risk, focusing only on individual advice is unlikely to be enough.
Improving access to healthy foods, limiting aggressive promotion of ultra processed products and designing walkable, safe neighbourhoods can complement person centred support.
For individuals, the study is a reminder to be realistic. If you live in an area dominated by takeaway outlets and poor transport, you are not imagining it; your environment probably is making healthy choices harder.
